I assume we are talking about the metal sealant stuff. I'm pretty sure there is no way to clean that out. it probably didn't fix the issue anyway. I'd be careful and make sure the coolant doesn't start getting into the cylinders.

Only way is to get a good hot tank cleaning. At that point it'll probably be cheaper to just get another engine. Some of those head gasket sealers work for a time, but cause irreversible damage in the long run.